Plane-surface piezo-electric loud speaker



Oct. 23, 1928.

A. M L. NICOLSON PLANE SURFACE PIEZO'-ELECTRIC LOUD SPEAKER Filed'March 11, 1927 YE E INVENTOR ALEXANDER MCLEAN NICULSON (46% G I ATTORNEY Patemed 192s.

ALEXANDER MCI-EAR NICOLSON, OF NEW 1116., OF NEW- YOBK, N. Y., A

YQBK, N. Y., ASSIGNOR Ti) ED RADIO; CORPQRATION F DELAWARE.

PLANE-SUREACE PIEZQ-ELECTRIG LUUD SEE I."

Application filed March 11, 1927. Serial No. I'M/M8.

This invention relates to, a loud speaker. adapted for. operation by electric currents and more particularly to a loud speaker comprising a piezo-elect-ric crystal.

It has been known fora considerable time that by subjecting certain crystals to pressure, ditferences in electrical potential between different parts or regions of the crystals may be produced, and that, conversely, when differences of potential'are applied to difierent parts of such crystals, they develop stresses or motion in accordance therewith. Such phenomena are termed piezo-electric activity and the crystals exhibiting such activity are termed piezo-elect-ric crystals.

Such piezo-electric qualities are not limited to whole crystals but may be manifested by plates or rods cut from the crystals in a suitable manner, as more particularly set *forth in my copen'ding application Serial No.

- 155,902, filed Dec. 20, 1926, entitled Orientation of component crystals'in composite piezoelectric devices. Although such effects may be obtained with crystals oia number of different substances, they are obtained in a marked degree from crystals of the substance known as Rochelle salt or sodium-potassiumtartrate.

An important object of the present inven- 30 tion is to provide a novel and effective loud speaker.

Another object of the invention is to provide a novel loud speaker making ,use of piezo-electric phenomena. Still a further object of my invention is to provide a loud speaker of high quality, which is relativelysimple and inexpensive to construct and reliable in operation.

In carrying out my invention, I may provide a piezo-electric crystal device having electrodes arranged thereon, in a manner to be hereafter explained more in detail, and havinq' conductors connected thereto for impressing on the said electrodes differences in potential corresponding to the sounds desired to be reproduced. The saidcrystal device is mounted or secured upon a relatively large and preferably plane surface,-such for example, as the top no of'a table, the vertical wall of a cabinet, or

the like, in such manner as to set the said surface into vibration in accordance with the vibrations of the crystal device.

In order to secure the best results, I have found that the crystal should not be directly attached to any relatively soft material, such as wood or the like, but should be attached to one or more metal plates which in turn are attached to the soft material.

The features of noveltywhich I believe to 6 be characteristic of my invention-are set forth with particularity in the appended claims. My invention itself, however, will best be understood both as to its fundamental principles and as to its practical embodiments by reference to the specification and accompanying drawing, in which:

Fig. 1 illustrates one embodiment of the invention; I

Fig. 2 illustrates a second embodiment of the invention; and

Fig. 3 illustrates an application of the invention to a radio set.

'As indicated in Fig.1. a piezo-electric crystal 1 preferably of Rochelle salt may be 5 utilized to set into vibration a relatively large surface of comparatively large mass, such. as the top 2'ofa table 3, thereby producing sound waves of relatively large power and volume. In this form the crystal 1 is suitably secured at each basal plane to a stress plate 4 of suitable material such as steel. The whole is secured against the under side of the table to 2 by means including bolts 5.

. The mem ers 4 may be secured to the crystal 1 by a bolt 4 passing through the members 4 and the crystal 1, and in addition the crystal may be cemented to the members by Rochelle salt melt comprising Rochelle salt from which the desired amount of water has been removed by heating it at a temperature above its melting point.

Suitable electrodes are provided which may, for example, take the form of an equatorial belt electrode 6 of metal foil or graphite paint forming a loop around the crystal parallel to the basal plane thereof, and constituting one electrode, and a second electrode which may be formed by/holt 4 or by one or both of the end members or stress plates 4.

The said electrodes are connected'to opposite terminals of a source 9 of electrical oscillations of sound? frequency, which may, for example beQthe output terminals of a radio receiver or amplifier or an electric phono- 1 graph.

The crystal 1 will be set into vibration by .the electrical oscillations, which vibrations will be transmitted through the stress plates 4 to the table top 2, whence they are communicated to the atmosphere in greatly amplified form. It is to be noted that in the case where the surface to be set into vibrations 1s wood,

or the like, best results are obtained when a metal stress member having a large bearing surface on the wood is interposed between the crystal and the wood. The exactreasons for this phenomenon are somewhat obscure, but apparently the wood is set into vibration only in local zones and the sound produced is lacking in quality and quantity if the crystal is mounted directly thereon, without the interposed metal member. because the crystal has a high motional impedance and requires a stifi coupling to stress the'wood, which is relatively softer.

Referring now to Fig. 2, I have shown a crystal 1 supported on the lower side of plate 11 which may be of metal, secured to a table top 2 by suitable bolts 12. In this form the crystal 1 is secured to the plate 11 by sultable means such as Rochelle salt melt. In this case, the electrodes of the crystal 1 shown diagrammatically, are connected with source 9 as before. It should be understood that this arrangementis particularly advantageous in that the plate 11 with the piezo-electrlc crystal mounted thereon may easily be shifted and attached to parts of furniture or other suitable members as desired.

Referring now to Fig. 3, I have shown a 'piezo-electric crystal 1 and plate 11 such as shown in Fig. 2, attached to a part ofthe cabinet 13 of a radio receiver 14. In this instance, the plate 11 is bolted or otherwise secured to the inside of the front panel. of the receiver cabinet, and the crystal electrodes are connected to the output terminals of the receiver.

It will be understood that this arrangement forms a particularly advantageous combination since it' provides for an inexpensive loud speaker of very high quality and good sound intensity, of the utmost simplicity to install,

which is crimpletely hidden from view, andyet radiates sound in practically all directions.

While I have illustrated only a few embodiments of my I invention, for the purpose of describing the same and illustrating its principles of operation, it is apparent that various changes and modifications may be made therein without departing fromthe spirit and scope of my invention. I desire, therefore, that only such limitations shall be imposed as are indicated by the prior art, or are specifically set forth in the appended claims.

I claim:

1. A loud speaker comprising a sound reproducing surface, a piezo-electric crystal evice adapted to be vibrated byelectrical oscillations of sound frequency, a metallic plate positioned parallel thereto, means con- This is probably necting opposite ends of said crystal device with said plate, and a bearing surface on said plate arranged for connection with said sound reproducing surface.

2. A loud speaker comprising a sound reproducing surface, a piezo-electric crystal device adapted to be vibrated by electrical oscillations of sound frequency, and a metal plate secured to said sound reproducing surface, said plate having a relatively large bearing surface co-extensive with said sound reproducing surface and connections between a pluralityof points on said crystal device and said plate.-

3. A loud speaker comprising a sound reproducing surface, a iezo-electric crystal device adapted to be vibrated by electrical oscillations, a metal plate connected through a plurality of independent points with said plate, said crystal "device being arranged to be mounted on said sound reproducing surface with the axis of said crystal parallel thereto whereby vibrations from said crystalare imparted to said sound reproducing surface. s Q

4. 'A'loud speaker comprising a sound reproducing surface, a piezo-electric crystal device adapted to be vibrated by electrical oscillations, a metal plate connected through a plurality of points with said plate, said crystal device being arranged to be mounted upon said sound reproducing surface. and to make contact therewith only through said metal plate. i

5. In a loud speaker, a wooden member adapted to be set into vibration, a piezo-electrio crystal of Rochelle salt adjacent said member, and means including Rochelle salt melt for connecting said crystal with said member at each end thereof.

6. In a loud speaker, a wooden member area in substantially the same plane adapted to be set into vibration, a metal plate, a piezoelectric crystal spaced from said plate but with its-opposite ends connected therewith, and means for detachably connecting said plate with said member for imparting vibrations thereto.

7. A loud speaker element adapted to be connected with a vibratile woodenmember and including a metallic supporting plate adapted to be secured to said member, a piezoelectric crystal substantially parallel to said plate but spaced therefrom and supports pro-' jecting from said plate and engaging the opposite ends of said crystal for transferring the vibrations of said crystal to said vibratile member. I

Signed at New York, in the county of New York and State of New York this. tenth day of March A. D. .1927.

ALEXANDER McLEAN NIGOLSON. 

